The Hawaiian spotted eagle ray is also known as the bonnet ray, the duck bill ray and the spotted duck billed ray, but perhaps no other name than hihimanu describes it better. This Hawaiian name means “magnificent’ or “elegant bird.” With the grace of an eagle, this cartilaginous fish can be found gliding in shallow coastal waters ranging throughout the Hawaiian island chain to at least Midway Atoll. The maximum span of their “wings”, or pectoral fins, is six feet from tip to tip and their coloration is stunning. White spots adorn a solid black background creating a dramatic topside pattern. The belly is a brilliant white with a black, geometric maze pattern on the underside of each wing. The wing tips have been observed breaking the water’s surface as the prelude to a breathtaking skyward launch, followed by an end over end mid-air cartwheel display.
Although the spotted eagle ray has a long whip-like tail with one or more barbed spines at the base, it is not classified as a true stingray; Hawaii’s three species of stingrays display venomous spines much further down the length of their tail. Hawaiian eagle rays are considered to be very docile and will often swim away when approached by divers. However, the barbed spines can be extremely painful if touched.
The hihimanu feed in soft sand sediments, using their fleshy, shovel-shaped snout to dig up clams and oysters. The same electroreceptor system found in sharks and other rays, the ampullae of Lorenzini, works similar to a metal detector and assist in locating electrical fields given off by their often buried prey. These sensory pores, located under the jaw and snout, also enable them to sense the earth’s magnetic field and aid in navigation. Another sense that sharks and rays share is a water-motion detector system called the lateral line. Located in the lateral line canal, this system consists of a series of canals running along the side of the animal’s body. A series of cells called neuromasts interpret information through vibrational changes in the water allowing the ray to feel not only nearby prey, but approaching predators and its own movements as well.
Spotted eagle rays feed on snails, shrimp, crabs, and sea urchins. Their flat, hard teeth plates are specially equipped to crush the shells of their prey. The shells are then spat out and the remaining meat is swallowed. Researchers have observed that the male teeth plates are slightly more pointed than the females. This may lend itself to the mating ritual in which the male bites the trailing edge of her wing and holds on during mating (which lasts approximately one minute).
These rays reach reproductive maturity at four to six years of age. Embryos develop only in the left uterus where they are nourished by uterine milk. Hihimanu give live birth to a litter of one to four pups, each displaying a 10-20 inch wingspan. Exciting aerial displays have been associated with the birthing process, in which the mother leaps out of the water and expels the pups in mid-air. The newborns arrive with their wings wrapped bat-like around their bodies. They quickly unfold and begin to swim to avoid their main predators, the sharks.
In addition to sharks (primarily the tiger shark in Hawaii), main threats are fishing, accidental by-catch, and entanglement. Although their flesh is edible, it is not desirable, and they are more often sought after for oil or fishmeal.
*Due to the constant rotation of animals back to the ocean, the presence of any specific animal cannot be guaranteed.